I've Googled the cause of this, but all I find are threads about front derailleur adjustment and not cross-chaining. Duh. I have a slightly different problem. I have an old cheapish square taper crankset that I've been using on my vintage road bike. Every time I put down the power (probably about 400 watts max), the big ring rubs BOTH sides of the front derailleur. This also happens sometimes when I am just cruising along. Yes, I have trimmed the derailleur, it's right smack in the middle. I'm not cross chaining. This happens even in 52x14. My front derailleur is aligned with the CHAIN, so it's perfectly straight. If I raise my derailleur, the shifting becomes unpredictable. Is it a square taper problem, or cheap crank problem? I have a two-piece shimano crankset that I can use, but I would prefer to keep the vintage styling.